1. Field of the Invention
The present invention relates to an auto-focus device, a projection lens device, and an image projection apparatus.
2. Description of the Related Art
Conventionally, there is known an image projection apparatus that generates an image to be projected at an image forming unit by using a light emitted from a light source on the basis of image data received from a personal computer or a video camera, etc. and projects the generated image on a projection target surface, such as a screen, to display the image on the projection target surface. Such an image projection apparatus is required to be capable of projecting an image on a large screen and reducing a distance between the image projection apparatus and the projection target surface as much as possible, and image projection apparatuses enabling a short projection distance have been developed.
For example, an image projection apparatus disclosed in Japanese Patent Application Laid-open No. H10-325982 is equipped with an auto-focus device that automatically adjusts the focus of a projected image. The auto-focus device is equipped with a light source for measurement of a distance to a projection target surface separately from a light source device for projecting an image. A light emitted from the light source is reflected by the projection target surface, and a diffusely-reflected light reflected from the projection target surface is received by a light receiving element installed in the auto-focus device. The auto-focus device automatically changes the focus position of a projection lens by calculating a focal distance to the projection target surface from the received diffusely-reflected light.
In the auto-focus device as described above, an amount of received diffusely-reflected light varies depending on the position of the light receiving element installed in the auto-focus device; therefore, accuracy in the installation of the light receiving element is required. However, in the conventional installation of the light receiving element, the light receiving element is directly bonded to a housing of the auto-focus device, which results in inefficient workability and causes a decrease in work efficiency and reduction in the accuracy.
In view of the above, there is a need to provide an auto-focus device that allows accurate installation of a light receiving element.